That figure is vastly over estimated, in reality.
The jewels were being inventoried for sale so overvaluing was to that aim- make the most money.
Also Twining I think it is, states that the jewels, though indeed impressive, were essentially of low quality gem stones.
There was a glut in the market at that time and values were not reached [Greatest Heist]
The vast majority of her collection was in the form od gifts, Wedding, Coronation, births, anniversaries, visit, etc. She di not buy this stuff.
There are 2 sides of a mirror.